Volunteers will be screened and admitted to our inpatient clinical research unit. They will undergo baseline measurements of glucose tolerance, food intake and energy expenditure in a whole room indirect calorimeter. After randomization to active drug or placebo, these measurements will be repeated. After the baseline admission, volunteers will be followed as outpatients initially on a weekly basis (for one month), followed by a monthly basis for another 5 months. Volunteers will then be readmitted for repeat measurements of food intake. All volunteers will then have the option of open label use of exenatide for another 6 months during which time they will again be followed monthly. Our goal is to recruit 100 subjects and 32 are currently enrolled or have completed the study. Mean weight loss (regardless of randomization which is blinded until study end) is 1.7 kg.